Optical fiber

ABSTRACT

An optical fiber includes a glass portion, a primary coating layer, and a secondary coating layer. In the optical fiber, a value of microbend loss characteristic factor F μBL_GΔβ  is 6.1 ([GPa −1 ·μm −2.5 /rad 8 ]·10 −12 ) or less when represented by 
         F   μBL_GΔβ   =F   μBL_G   ×F   μBL_Δβ , 
     where F μBL_G  is geometry microbend loss characteristic and F μBL_Δβ  is optical microbend loss characteristic.

TECHNICAL FIELD

The present invention relates to an optical fiber, specifically, to anoptical fiber that can be used for an optical fiber cable.

BACKGROUND

In recent years, the traffic of communication infrastructuresconstructed by optical fiber cables and the like has been increasing dueto the maturity of Fiber To The Home (FTTH) services, the spread ofmobile terminals, the expansion of cloud service usage, the increase invideo traffic, and the like. Therefore, it is demanded to constructcommunication infrastructures more economically and efficiently thanbefore. Under such background, there is a demand to increase the numberof mounting cores and mounting density of optical fibers mounted inoptical fiber cables.

As a means for increasing the number of mounting cores and mountingdensity of the optical fibers, it is conceivable to reduce the diameterof the optical fibers. However, in this case, the optical fibers areeasily affected by the lateral pressure, and the microbend loss, whichis the optical loss caused by the shaft of the optical fibers beingslightly bent, namely microbending, can be large. Patent Literature 1below describes that the elastic modulus and the glass transition pointof an optical fiber coating are adjusted to reduce the coating thicknessof the optical fiber so that the microbend loss can be suppressed evenwhen the diameter of the optical fiber is reduced.

-   [Patent Literature 1] JP 2012-508395 A

However, the aforementioned microbend loss tends to be affected byparameters related to the geometry of the optical fiber such as thecoating thickness of the optical fiber, the outside diameter of theglass forming the core and the clad, the Young's modulus of theaforementioned glass, and the Young's modulus of the coating, andparameters related to the optical characteristics of the optical fibersuch as the propagation constant of light propagating through theoptical fiber. In Patent Literature 1 described above, the coatingthickness is taken into consideration as the aforementioned parameter interms of suppressing microbend loss, but the parameters other than thecoating thickness are not taken into consideration. Therefore, there isa demand for an optical fiber capable of suppressing microbend loss thattakes into consideration various parameters that affect microbend loss.

The present invention provides an optical fiber capable of suppressingmicrobend loss.

SUMMARY

One or more embodiments of the present invention provide an opticalfiber including a glass portion including a core and a clad surroundingthe core, a primary coating layer covering the clad, and a secondarycoating layer covering the primary coating layer,

in which

a value of microbend loss characteristic factor F_(μBL_GΔβ)([GPa⁻¹·μm^(−2.5)/rad⁸]·10⁻¹²) represented by

F _(μBL_GΔβ) =F _(μBL_G) ×F _(μBL_Δβ)

by using

geometry microbend loss characteristic F_(μBL_G)(GPa⁻¹·μm^(−10.5)·10⁻²⁷) of the optical fiber represented by

$F_{\mu{BL}\_ G} = \frac{{K_{s}}^{2}}{{H_{f}}^{2} \times {D_{0}}^{0.375} \times {H_{0}}^{0.625}}$${K_{s} = \frac{E_{p}d_{f}}{t_{p}}},{H_{f} = {\frac{\pi}{4}{E_{g}\left( \frac{d_{f}}{2} \right)}^{4}}},{D_{0} = {E_{p} + {\left( \frac{t_{s}}{R_{s}} \right)^{3}E_{s}}}},{H_{0} = {\frac{\pi}{4}{E_{s}\left( {{R_{s}}^{4} - {R_{p}}^{4}} \right)}}}$

when a spring coefficient of the primary coating layer is κs (MPa), abending rigidity of the glass portion is H_(f) (MPa·μm⁴), a deformationresistance of the secondary coating layer is D₀ (MPa), a bendingrigidity of the secondary coating layer is H₀ (MPa·μm⁴), a Young'smodulus of the glass portion is E_(g) (GPa), a Young's modulus of theprimary coating layer is E_(p) (MPa), a Young's modulus of the secondarycoating layer is E_(s) (MPa), an outside diameter of the glass portionis d_(f) (μm), a radius of an outer peripheral surface of the primarycoating layer is R_(p) (μm), a radius of an outer peripheral surface ofthe secondary coating layer is R_(s) (μm), a thickness of the primarycoating layer is t_(p) (μm), and a thickness of the secondary coatinglayer is t_(s) (μm), and

optical microbend loss characteristic F_(μBL_Δβ) (1/(rad/μm)⁸) of theoptical fiber represented by

$F_{\mu{BL}{\_\Delta\beta}} = \frac{1}{({\Delta\beta})^{8}}$

when a difference between propagation constant of a waveguide modepropagating through the optical fiber and propagation constant of aradiation mode is propagation constant difference Δβ (rad/m),

is 6.1 ([GPa⁻¹·μm^(−2.5)/rad⁸]·10⁻¹²) or less.

The microbend loss of optical fiber is, as described in Non-PatentLiterature 1 (J. Baldauf, et al., “Relationship of MechanicalCharacteristics of Dual Coated Single Mode Optical Fibers andMicrobending Loss,” IEICE Trans. Commun., vol. E76-B, No. 4, 1993.),Non-Patent Literature 2 (K. Petermann, et al., “Upper and Lower Limitsfor the Microbending Loss in Arbitrary Single-Mode Fibers,” J. Lightwavetechnology, vol. LT-4, no. 1, pp. 2-7, 1986.), Non-Patent Literature 3(Okoshi et al. “Optical Fiber,” Ohmsha, pp. 235-239, 1989.), andNon-Patent Literature 4 (P. Sillard, et al., “Micro-Bend Losses ofTrench-Assisted Single-Mode Fibers,” ECOC2010, We.8.F.3, 2010.), tendsto be affected by both the geometry and the optical characteristics ofthe optical fiber.

Here, the geometry of the optical fiber is a parameter related to thestructure of the optical fiber, and, in one or more embodiments of thepresent invention, the spring coefficient Ks of a primary coating layerof the optical fiber, the bending rigidity H_(f) of a glass portion, thedeformation resistance Do of a secondary coating layer, the bendingrigidity H₀ of the secondary coating layer, the Young's modulus E_(g) ofthe glass portion, the Young's modulus E_(p) of the primary coatinglayer, the Young's modulus E_(s) of the secondary coating layer, theoutside diameter d_(f) of the glass portion (diameter of the glassportion), the radius R_(p) of the primary coating layer, the radiusR_(s) of the secondary coating layer, the thickness t_(p) of the primarycoating layer, and the thickness t_(s) of the secondary coating layer.

By the way, according to Non-Patent Literature 2 to 4 described above,the microbend loss is a phenomenon caused by mode coupling in which awaveguide mode propagating through the optical fiber is coupled with aradiation mode. Such mode coupling is considered to occur due to theaforementioned microbending, and is said to be determined by apropagation constant difference (Δβ), which is the difference betweenthe propagation constant of the waveguide mode of light propagatingthrough the optical fiber and the propagation constant of the radiationmode. The above-mentioned optical characteristics of the optical fiberare parameters related to the characteristics of light propagatingthrough the optical fiber, and in one or more embodiments of the presentinvention, mean the aforementioned propagation constant difference Δβ(rad/m).

The microbend loss of such an optical fiber may be represented by thevalue of sandpaper tension winding loss increase, which is thedifference between the transmission loss measured in a state where theoptical fiber is wound in one layer with a predetermined tension on aroughened bobbin body portion and the transmission loss measured in astate where the optical fiber is unwound from the bobbin with almost notension applied. The smaller the value of such sandpaper tension windingloss increase becomes, the smaller is the microbend loss of the opticalfiber.

By the way, as an optical fiber cable constituting communicationinfrastructures, a so-called tape slot type cable (RSCC: Ribbon SlottedCore Cable) including a plurality of tape core wires accommodated ineach of a plurality of slots formed on a holding body for holding thetape core wires and a small-diameter high-density cable (UHDC:Ultra-High Density Cable) including tape core wires densely arrangedinside the cable without using the aforementioned holding body areknown. Of these, since the tape slot type cable has a structure in whicha plurality of tape core wires are accommodated in the slots asdescribed above, a lateral pressure is applied to the optical fibersconstituting the tape core wires, which may cause microbend loss.Therefore, in the tape slot type cable, in consideration of suchmicrobend loss, an optical fiber in which the value of sandpaper tensionwinding loss increase is suppressed to 0.6 dB/km or less may be used.

The present inventor has diligently studied the relationship between thesandpaper tension winding loss increase and the aforementioned variousparameters regarding the optical fiber used for the optical fiber cable.As a result, it was found that the value of microbend losscharacteristic factor F_(μBL_GΔβ) represented by the aforementionedformula has a high correlation with the value of sandpaper tensionwinding loss increase. That is, the present inventor has found that thevalue of the microbend loss characteristic factor has a substantiallypositive slope proportional relationship with the value of sandpapertension winding loss increase.

Furthermore, the present inventor has conducted further research andfound that when the value of the aforementioned microbend losscharacteristic factor is 6.1 ([GPa⁻¹·μm^(−2.5)/rad⁸]·10⁻¹²), the valueof the sandpaper tension winding loss increase is a value slightlysmaller than 0.6 dB/km. As described above, the value of the microbendloss characteristic factor has a substantially positive slopeproportional relationship with the value of sandpaper tension windingloss increase. Therefore, by setting the value of the microbend losscharacteristic factor of the optical fiber to 7183 GPa³·nm^(2.5)·rad⁸ orless, the microbend loss can be suppressed to the extent that theoptical fiber can be applied to the tape slot type cable.

As described above, with the optical fiber of one or more embodiments ofthe present invention, the microbend loss can be suppressed.

Furthermore, the value of the microbend loss characteristic factor maybe 4.1 ([GPa⁻¹·μm^(−2.5)/rad⁸]·10⁻¹²) or less.

Among the optical fiber cables constituting the communicationinfrastructures, in the small-diameter high-density cable, the tape corewires are densely arranged as described above. Therefore, similar to thetape slot type cable, the optical fiber constituting the tape core wireis subjected to a lateral pressure, and the microbend loss can occur.Furthermore, since the small-diameter high-density cable is slotless asdescribed above and all the tape core wires are densely arranged insidethe cable, the optical fiber tends to be subjected to a large lateralpressure as compared with the tape slot type cable in which the tapecore wires are separately arranged in a plurality of grooves. Therefore,in the small-diameter high-density cable, it is recommended to use anoptical fiber having a smaller microbend loss than the optical fiberused for the tape slot type cable. In view of the above, in thesmall-diameter high-density cable, an optical fiber in which the valueof sandpaper tension winding loss increase is suppressed to 0.34 dB/kmor less may be used.

The present inventor has found that the value of the microbend losscharacteristic factor substantially corresponding to the value (0.34dB/km) of the sandpaper tension winding loss increase is 4.1([GPa⁻¹·μm^(−2.5)/rad⁸]·10⁻¹²). Therefore, by setting the value of themicrobend loss characteristic factor of the optical fiber to 4.1([GPa⁻¹·μm^(−2.5)/rad⁸]·10⁻¹²) or less, the microbend loss can besuppressed to the extent that the optical fiber can also be applied tothe small-diameter high-density cable.

Furthermore, in the aforementioned optical fiber, the coating thicknessof a sum of the thickness of the primary coating layer and the thicknessof the secondary coating layer may be 42.0 μm or less.

The larger the aforementioned coating thickness becomes, the larger theoutside diameter of the optical fiber tends to be, and the smaller thecoating thickness becomes, the smaller the outside diameter of theoptical fiber tends to be. The optical fiber used for the optical fibercable constituting the communication infrastructures generally has acoating thickness of approximately 60 μm. Therefore, when the coatingthickness is 42.0 μm or less, it is possible to realize an optical fiberhaving a smaller diameter than a general optical fiber constituting thecommunication infrastructures. By the way, the value of the microbendloss characteristic factor is determined by various parameters asdescribed above, and the parameters include the thickness of the primarycoating layer and the thickness of the secondary coating layer.Therefore, according to one or more embodiments of the presentinvention, even when the thickness of the primary coating layer or thethickness of the secondary coating layer is reduced, the value of themicrobend loss characteristic factor can be 6.1([GPa⁻¹·μm^(−2.5)/rad⁸]·10⁻¹²) or less or can be 4.1([GPa⁻¹·μm^(−2.5)/rad⁸]·10⁻¹²) or less by adjusting other parameters.Therefore, even when the coating thickness of the optical fiber of thepresent invention is 42.0 μm or less, the microbend loss can besuppressed to the extent that the optical fiber can be used for the tapeslot type cable or the small-diameter high-density cable.

Furthermore, the coating thickness may be 38.0 μm or less.

Furthermore, the coating thickness may be 36.5 μm or less.

Furthermore, the coating thickness may be 34.5 μm or less.

Furthermore, the coating thickness may be 34.0 μm or less.

By reducing the coating thickness in this way, the microbend loss can besuppressed to the extent that the optical fiber can be used for the tapeslot type cable or the small-diameter high-density cable, and an opticalfiber with a smaller diameter can be realized.

Furthermore, when the coating thickness is 42.0 μm or less, the outsidediameter of the glass portion may be 65 μm or more and 100 μm or less.

The larger the outside diameter of the aforementioned glass portionbecomes, the larger the outside diameter of the optical fiber tends tobe, and the smaller the outside diameter of the glass portion becomes,the smaller the outside diameter of the optical fiber tends to be. Theoptical fiber used for the optical fiber cable constituting thecommunication infrastructures is generally formed such that the outsidediameter of the glass portion is 125 μm. Therefore, when the coatingthickness is 42.0 μm or less and the outside diameter of the glassportion is 100 μm or less, it is possible to realize an optical fiberhaving a smaller diameter than a general optical fiber constituting thecommunication infrastructures. By the way, the value of the microbendloss characteristic factor is determined by various parameters asdescribed above, and the parameters include the coating thickness andthe outside diameter of the glass portion. Therefore, according to oneor more embodiments of the present invention, even when the coatingthickness is reduced and the outside diameter of the glass portion isreduced, the value of the microbend loss characteristic factor can be6.1 ([GPa⁻¹·μm^(−2.5)/rad⁸]·10⁻¹²) or less or can be 4.1([GPa⁻¹·μm^(−2.5)/rad⁸]·10⁻¹²) or less by adjusting other parameters.Therefore, even when the coating thickness of the optical fiber of thepresent invention is 42.0 μm or less and the outside diameter of theglass portion is 100 μm or less, the microbend loss can be suppressed tothe extent that the optical fiber can be used for the tape slot typecable or the small-diameter high-density cable.

Note that when the outside diameter of a glass portion havingbrittleness is as thin as approximately 65 μm, the mechanical bendingresistance of the optical fiber can be increased by the amount that thebrittle glass is thinned.

Furthermore, the outside diameter of the glass portion may be 90 μm orless.

Furthermore, the outside diameter of the glass portion may be 80 μm orless.

Furthermore, the outside diameter of the glass portion may be 75 μm orless.

Furthermore, the outside diameter of the glass portion may be 70 μm orless.

By reducing the outside diameter of the glass portion in this way, themicrobend loss can be suppressed to the extent that the optical fibercan be used for the tape slot type cable or the small-diameterhigh-density cable, and an optical fiber with a far smaller diameter canbe realized.

Furthermore, when the aforementioned coating thickness is 42.0 μm orless, the mode field diameter at a wavelength of 1310 nm may be 7.6 μmor more and 8.7 μm or less, the cable cutoff wavelength may be 1260 nmor less, the zero dispersion wavelength may be 1300 nm or more and 1324nm or less, and the zero dispersion slope may be 0.073 ps/km/nm or moreand 0.092 ps/km/nm.

In this case, the macrobend loss at a wavelength of 1625 nm by bendingat a radius of 10 mm may be 1.5 dB/turn or less.

Alternatively, the macrobend loss at a wavelength of 1625 nm by bendingat a radius of 10 mm may be 0.2 dB/turn or less.

Alternatively, the macrobend loss at a wavelength of 1625 nm by bendingat a radius of 10 mm may be 0.1 dB/turn or less.

As described above, according to one or more embodiments of the presentinvention, there is provided an optical fiber capable of suppressing themicrobend loss.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram schematically showing a structure of a cross sectionperpendicular to a longitudinal direction of an optical fiber cableaccording to a first embodiment of the present invention.

FIG. 2 is a perspective view schematically showing an example of anoptical fiber tape core wire included in the optical fiber cable shownin FIG. 1.

FIG. 3 is a diagram schematically showing a structure of a cross sectionperpendicular to the longitudinal direction of the optical fiberincluded in the optical fiber tape core wire shown in FIG. 2.

FIG. 4 is a diagram showing a structure of a cross section perpendicularto a longitudinal direction of an optical fiber cable according to asecond embodiment of the present invention.

FIG. 5 is a diagram showing a relationship between a value of microbendloss characteristic factor and sandpaper tension winding loss increasein the optical fiber shown in FIG. 3.

DETAILED DESCRIPTION

Aspects for carrying out the optical fiber according to the presentinvention will be illustrated below together with the accompanyingdrawings. The embodiments illustrated below are for facilitating theunderstanding of the present invention, and are not for limiting theinterpretation of the present invention. The present invention can bechanged or modified from the embodiments below without departing fromthe spirit. Furthermore, in the present specification, the dimensions ofeach member may be exaggerated for ease of understanding.

First Embodiment

FIG. 1 is a diagram schematically showing a structure of a cross sectionperpendicular to a longitudinal direction of an optical fiber cable 1according to the first embodiment. As shown in FIG. 1, the optical fibercable 1 is a so-called tape slot type cable (RSCC: Ribbon Slotted CoreCable). The optical fiber cable 1 includes a sheath 3, a plurality oftape core wires 4, a holding body 5, and a tensile strength body 6 asmain configurations.

The sheath 3 is a tubular member and may be formed of a thermoplasticresin such as polyethylene. The aforementioned holding body 5 isaccommodated in the internal space of the sheath 3. In this way, thesheath 3 accommodates the holding body 5 inside and protects the holdingbody 5.

The holding body 5 is a member that holds the plurality of tape corewires 4. A plurality of slots 5S are formed on the holding body 5, andthe plurality of tape core wires 4 are accommodated in the slots 5S.Note that by increasing the number of tape core wires 4 accommodated inthe slots 5S, the number of cores of optical fiber included in theoptical fiber cable 1 can be increased.

In the present embodiment, the tensile strength body 6 is embedded inthe substantially center of the holding body in the cross-sectional viewof FIG. 1. Such tensile strength body 6 can suppress the tape core wires4 from being stretched more than necessary when tension is applied inthe longitudinal direction of the tape core wires 4.

FIG. 2 is a perspective view schematically showing an example of thetape core wire 4. As shown in FIG. 2, the tape core wire 4 of thepresent embodiment is a so-called intermittent adhesive type tape corewire. The tape core wire 4 has a configuration in which a plurality ofoptical fibers 10 are arranged along a direction perpendicular to thelongitudinal direction, and the arranged optical fibers 10 are adheredto each other. The tape core wire 4 includes adhesive portions 4A andsingle core portions 4B. The adhesive portion 4A is a portion whereadjacent optical fibers 10 are adhered to each other, and is providedintermittently at a constant pitch along the longitudinal direction. Thesingle core portion 4B is a portion located between the adhesiveportions 4A, and is a portion where the optical fibers 10 are notadhered to each other. With such a configuration, the tape core wire 4can be easily deformed, for example, twisted or bundled in asubstantially cylindrical shape. FIG. 1 schematically shows a state inwhich each tape core wire 4 is bundled in a substantially cylindricalshape.

Note that FIG. 2 shows an example in which the tape core wire 4 includesfour optical fibers 10, but this is an example. That is, the number ofoptical fibers 10 constituting the tape core wire 4 is not particularlylimited, and may be less than four or may be more than four. Forexample, the tape core wire 4 may include 12-core optical fibers 10.Furthermore, the tape core wire 4 is not limited to the intermittentadhesive type.

FIG. 3 is a diagram showing a structure of a cross section perpendicularto the longitudinal direction of the optical fiber 10 constituting thetape core wire 4. The optical fiber 10 of the present embodiment is asingle-mode optical fiber. As shown in FIG. 3, the optical fiber 10includes a core 11, a clad 12 that surrounds the core 11 without gaps, aprimary coating layer 14 that covers the clad 12, and a secondarycoating layer 15 that covers the primary coating layer 14 as the mainconfigurations. In the optical fiber 10, the clad 12 has a lowerrefractive index than the core 11.

The core 11 may be formed of pure quartz to which no dopant has beenadded, or may be formed of quartz to which germanium (Ge) or the likethat increases the refractive index has been added as a dopant.

The clad 12 has a lower refractive index than the core 11 as describedabove. For example, when the core 11 is formed of pure quartz, the clad12 may be formed of quartz to which fluorine (F), boron (B), or the likethat lowers the refractive index has been added as a dopant, and whenthe core 11 is formed of quartz to which germanium (Ge) or the like thatincreases the refractive index has been added as a dopant, the clad 12may be formed of pure quartz to which no dopant has been added.Furthermore, the clad 12 may be formed of quartz to which chlorine (Cl2)has been added. Furthermore, the clad 12 may be a single layer, mayinclude a plurality of layers having different refractive indexes, ormay be a hole-assisted type.

As described above, the core 11 and the clad 12 are both formed ofquartz (glass). Therefore, the core 11 and the clad 12 are collectivelyreferred to as a glass portion 13. That is, the glass portion 13includes the core 11 and the clad 12, and the glass portion 13 iscovered with the primary coating layer 14. Note that the glass portion13 is sometimes also referred to as an optical fiber bare wire portion.The outside diameter (diameter) d_(f) of such glass portion 13 isgenerally 125 μm. However, in the present embodiment, the outsidediameter d_(f) of the glass portion 13 can be a smaller outsidediameter. For example, it can be 65 μm or more and 100 μm or less, 65 μmor more and 90 μm or less, 65 μm or more and 80 μm or less, 65 μm ormore and 75 μm or less, or 65 μm or more and 70 μm or less. The reasonwhy the outside diameter d_(f) of the glass portion 13 can be small inthis way will be described later.

Note that when the outside diameter d_(f) of a glass portion havingbrittleness is as thin as approximately 65 μm, the mechanical bendingresistance of the optical fiber can be increased by the amount that thebrittle glass is thinned.

The primary coating layer 14 is formed of, for example, an ultravioletcurable resin or a thermosetting resin, and is formed on an outer sideof the glass portion 13 with a thickness t_(p) (μm). In the presentembodiment, the Young's modulus E_(g) of the primary coating layer 14 islower than the Young's modulus E_(s) of the secondary coating layer 15.By setting the primary coating layer 14 in direct contact with the glassportion to have a low Young's modulus in this way, the primary coatinglayer 14 acts as a cushioning material, and the external force acting onthe glass portion 13 can be reduced. Note that assuming that the radiusof the outer peripheral surface of the primary coating layer 14 is R_(p)(μm), the outside diameter of the primary coating layer 14 isrepresented by 2R_(p), and assuming that the radius (d_(f)×1/2) of theglass portion is R_(g) (μm), the aforementioned thickness t_(p) of theprimary coating layer 14 is represented by the formula described below.

t _(p) =R _(p) −R _(g)

In the present embodiment, the secondary coating layer 15 is a layerforming the outermost layer of the optical fiber 10, and is formed of,for example, an ultraviolet curable resin or a thermosetting resindifferent from the type of resin forming the primary coating layer 14,and is formed on an outer side of the primary coating layer 14 with athickness t_(s) (μm). For example, when the primary coating layer 14 isformed of an ultraviolet curable resin, the secondary coating layer 15may be formed of an ultraviolet curable resin different from theultraviolet curable resin forming the primary coating layer 14, and whenthe primary coating layer 14 is formed of a thermosetting resin, thesecondary coating layer 15 may be formed of a thermosetting resindifferent from that of the primary coating layer 14. In the presentembodiment, the Young's modulus E_(s) of the secondary coating layer 15is higher than the Young's modulus E_(g) of the primary coating layer14. As described above, by setting the secondary coating layer 15forming the outermost layer of the optical fiber 10 to have a highYoung's modulus, the glass portion 13 can be appropriately protectedfrom the external force. Note that assuming that the radius of the outerperipheral surface of the secondary coating layer 15 is R_(s), theoutside diameter of the secondary coating layer 15, i.e., the outsidediameter of the optical fiber 10 is represented by 2R_(s), and theaforementioned thickness t_(s) of the secondary coating layer 15 isrepresented by the formula described below.

t _(s) =R _(s) −R _(p)

By the way, the outside diameter of the optical fiber used for theoptical fiber cable is generally approximately 240 μm to 250 μm.Therefore, the outside diameter of the secondary coating layer 15 may beapproximately 240 μm. However, in the present embodiment, the outsidediameter of the secondary coating layer 15 can be smaller than 240 μm.For example, it can be approximately 190 μm, approximately 150 μm toapproximately 160 μm, or approximately 125 μm. The reason why theoutside diameter of the secondary coating layer 15, i.e., the outsidediameter of the optical fiber 10 can be small in this way will bedescribed later.

Furthermore, assuming that the sum of the thickness t_(p) of the primarycoating layer 14 and the thickness t_(s) of the secondary coating layer15 is the coating thickness t, the coating thickness of the opticalfiber used for the optical fiber cable is generally approximately 60 μm.Therefore, the coating thickness t of the optical fiber 10 may beapproximately 60 μm. However, in the present embodiment, the coatingthickness t of the optical fiber 10 can be smaller than 60 μm. Forexample, it can be 42.5 μm or less, 38.0 μm or less, 36.5 μm or less,34.5 μm or less, or 34.0 μm or less. The reason why the coatingthickness of the optical fiber 10 can be small in this way will bedescribed later.

As described above, in the optical fiber cable 1 of the presentembodiment, the tape core wires 4 including a plurality of such opticalfibers 10 are densely accommodated in the slots 5S of the holding body5. As a result, the optical fiber cable 1 can accommodate a large numberof cores of optical fiber. For example, the optical fiber cable 1accommodates 1000-core or more optical fibers. Furthermore, as describedabove, in the optical fiber 10 of the present embodiment, the glassportion 13 can be formed to have an outside diameter smaller than thatof the glass portion of a general optical fiber, and the coatingthickness can be formed to be smaller than the coating thickness of ageneral optical fiber. Therefore, the outside diameter of the opticalfiber 10 can be smaller than the outside diameter of a general opticalfiber, and the diameter of the optical fiber 10 can be reduced. Byreducing the diameter of the optical fiber 10 in this way, the size ofthe tape core wire 4 can be smaller than the size of a general tape corewire. Therefore, the tape core wires 4 having such a small size areaccommodated in the slots 5S, and the number of cores of optical fiberaccommodated in the optical fiber cable 1 can be further increased.Alternatively, the tape core wires 4 having such a small size areaccommodated in the slots 5S, and the size of the optical fiber cable 1can be reduced.

On the other hand, as the accommodation density of the tape core wiresin the slots increases, the lateral pressure acting on the optical fibertends to increase. When the optical fiber receives the lateral pressurein this way, the shaft of the optical fiber is slightly bent, and themicrobend loss can occur. Furthermore, when the outside diameter of theglass portion of the optical fiber or the coating thickness of theoptical fiber is reduced, the glass portion is susceptible to thelateral pressure, and eventually the microbend loss can occur.

However, the optical fiber 10 of the present embodiment is formed sothat the value of the microbend loss characteristic factor F_(μBL_GΔβ)described later is 6.1 ([GPa⁻¹·μm^(−2.5)/rad⁸]·10⁻¹²) or less.Therefore, even when the outside diameter of the glass portion and thecoating thickness are reduced and the number of cores of the opticalfiber 10 accommodated in the slots 5S is increased, the microbend losscan be suppressed. The reason for this will be described in detailbelow.

The microbend loss of optical fiber is, as described in Non-PatentLiterature 1 (J. Baldauf, et al., “Relationship of MechanicalCharacteristics of Dual Coated Single Mode Optical Fibers andMicrobending Loss,” IEICE Trans. Commun., vol. E76-B, No. 4, 1993.),Non-Patent Literature 2 (K. Petermann, et al., “Upper and Lower Limitsfor the Microbending Loss in Arbitrary Single-Mode Fibers,” J. Lightwavetechnology, vol. LT-4, no. 1, pp. 2-7, 1986.), Non-Patent Literature 3(Okoshi et al. “Optical Fiber,” Ohmsha, pp. 235-239, 1989.), andNon-Patent Literature 4 (P. Sillard, et al., “Micro-Bend Losses ofTrench-Assisted Single-Mode Fibers,” ECOC2010, We.8.F.3, 2010.), tendsto be affected by both the geometry and the optical characteristics ofthe optical fiber.

Here, the geometry of the optical fiber is a parameter related to thestructure of the optical fiber, and is, in the present embodiment, thespring coefficient κs of the primary coating layer of the optical fiber,the bending rigidity H_(f) of the glass portion, the deformationresistance Do of the secondary coating layer, the bending rigidity H₀ ofthe secondary coating layer, the Young's modulus E_(g) of the glassportion, the Young's modulus E_(p) of the primary coating layer, theYoung's modulus E_(s) of the secondary coating layer, the outsidediameter d_(f) of the glass portion (diameter of the glass portion), theradius R_(p) of the primary coating layer, the radius R_(s) of thesecondary coating layer, the thickness t_(p) of the primary coatinglayer, and the thickness t_(s) of the secondary coating layer.

By the way, according to Non-Patent Literature 2 to 4 described above,the microbend loss is a phenomenon caused by mode coupling in which awaveguide mode propagating through the optical fiber is coupled with aradiation mode. This waveguide mode is, for example, LP01 mode. Suchmode coupling is said to occur due to the slight bending of the shaft ofthe optical fiber, namely microbending, and is considered to bedetermined by the propagation constant difference (Δβ), which is thedifference between the propagation constant in the waveguide mode andthe propagation constant in the radiation mode. The above-mentionedoptical characteristics of the optical fiber are parameters related tothe characteristics of light propagating through the optical fiber, andin the present invention, mean the aforementioned propagation constantdifference Δβ (rad/m).

The microbend loss of such an optical fiber may be represented by thevalue of sandpaper tension winding loss increase, which is thedifference between the transmission loss measured in a state where theoptical fiber is wound in one layer with a predetermined tension on aroughened bobbin body portion and the transmission loss measured in astate where the optical fiber is unwound from the bobbin with almost notension applied. The smaller the value of such sandpaper tension windingloss increase becomes, the smaller is the microbend loss of the opticalfiber.

By the way, the tape slot type cable (RSCC) such as the optical fibercable 1 of the present embodiment can cause the microbend loss asdescribed above. Therefore, the tape slot type cable has the requiredcharacteristics that the value of sandpaper tension winding lossincrease is 0.6 dB/km or less in consideration of such microbend loss.

The relationship between the sandpaper tension winding loss increase andthe aforementioned various parameters regarding the optical fiber usedfor the optical fiber cable was studied. As a result, it was found thata value of microbend loss characteristic factor F_(μBL_GΔβ) representedby the formula (3) below

F _(μBL_GΔβ) =F _(μBL_G) ×F _(μBL_Δβ)  (3)

by using

geometry microbend loss characteristic F_(μBL_G) determined by theformula (1) below

$\begin{matrix}{{F_{\mu{BL}\_ G} = \frac{{K_{s}}^{2}}{{H_{f}}^{2} \times {D_{0}}^{1.125 - {0.25\mu}} \times {H_{0}}^{{0.25\mu} - 0.125}}}{{K_{s} = \frac{E_{p}d_{f}}{t_{p}}},{H_{f} = {\frac{\pi}{4}{E_{g}\left( \frac{d_{f}}{2} \right)}^{4}}},{D_{0} = {E_{p} + {\left( \frac{t_{s}}{R_{s}} \right)^{3}E_{s}}}},{H_{0} = {\frac{\pi}{4}{E_{s}\left( {{R_{s}}^{4} - {R_{p}}^{4}} \right)}}}}} & (1)\end{matrix}$

related to a spring coefficient Ks of the primary coating layer, abending rigidity H_(f) of the glass portion, a deformation resistance Doof the secondary coating layer, a bending rigidity H₀ of the secondarycoating layer, a Young's modulus E_(g) of the glass portion, a Young'smodulus E_(p) of the primary coating layer, a Young's modulus E_(s) ofthe secondary coating layer, an outside diameter d_(f) of the glassportion, a radius R_(p) of the outer peripheral surface of the primarycoating layer, a radius R_(s) of the outer peripheral surface of thesecondary coating layer, a thickness t_(p) of the primary coating layer,and a thickness t_(s) of the secondary coating layer, which areparameters related to geometry,

and

optical microbend loss characteristic F_(μBL_Δβ) determined by theformula (2) below

$\begin{matrix}{F_{\mu{BL}{\_\Delta\beta}} = \frac{1}{({\Delta\beta})^{2p}}} & (2)\end{matrix}$

related to a propagation constant difference Δβ, which is a parameterrelated to optical characteristics,

has a high correlation with the value of sandpaper tension winding lossincrease. That is, the present inventor has found that the value of themicrobend loss characteristic factor has a substantially positive slopeproportional relationship with the value of sandpaper tension windingloss increase.

Note that according to Non-Patent Literature 5 (K. Kobayashi, et al.,“Study of Microbending loss in thin coated fibers and fiber ribbons,”IWCS, pp. 386-392, 1993.), the typical value of the constant μ in theaforementioned formula (1) is “3”. Therefore, the aforementioned formula(1) becomes the formula (4) described below.

$\begin{matrix}{{F_{\mu{BL}\_ G} = \frac{{K_{s}}^{2}}{{H_{f}}^{2} \times {D_{0}}^{0.375} \times {H_{0}}^{0.625}}}{{K_{s} = \frac{E_{p}d_{f}}{t_{p}}},{H_{f} = {\frac{\pi}{4}{E_{g}\left( \frac{d_{f}}{2} \right)}^{4}}},{D_{0} = {E_{p} + {\left( \frac{t_{s}}{R_{s}} \right)^{3}E_{s}}}},{H_{0} = {\frac{\pi}{4}{E_{s}\left( {{R_{s}}^{4} - {R_{p}}^{4}} \right)}}}}} & (4)\end{matrix}$

Furthermore, according to Non-Patent Literature 2 described above andNon-Patent Literature 6 (C. D. Hussey, et al., “Characterization anddesign of single-mode optical fibres,” Optical and Quantum Electronics,vol. 14, no. 4, pp. 347-358, 1982.), the typical value of the constant pin the aforementioned formula (2) is “4”. Therefore, the aforementionedformula (2) becomes the formula (5) described below.

$\begin{matrix}{F_{\mu{BL}{\_\Delta\beta}} = \frac{1}{({\Delta\beta})^{8}}} & (5)\end{matrix}$

Furthermore, the present inventor has conducted further research andfound that when the value of the aforementioned microbend losscharacteristic factor is 6.1 ([GPa⁻¹·μm^(−2.5)/rad⁸]·10⁻¹²), the valueof the sandpaper tension winding loss increase is a value slightlysmaller than 0.6 dB/km. As described above, the value of the microbendloss characteristic factor has a substantially positive slopeproportional relationship with the value of sandpaper tension windingloss increase. Therefore, by setting the value of the microbend losscharacteristic factor of the optical fiber to 6.1([GPa⁻¹·μm^(−2.5)/rad⁸]·10⁻¹²) or less, the microbend loss can besuppressed to the extent that the required characteristics of the tapeslot type cable are satisfied.

As described above, the optical fiber 10 of the present embodiment isformed so that the value of the microbend loss characteristic factorF_(μBL_GΔβ) is 6.1 ([GPa⁻¹·μm^(−2.5)/rad⁸]·10⁻¹²) or less. Therefore, inthe optical fiber 10 of the present embodiment, the microbend loss canbe suppressed to the extent that the required characteristics of thetape slot type cable are satisfied. Therefore, the optical fiber cable 1using the optical fiber 10 can exhibit favorable opticalcharacteristics.

Furthermore, as described above, in the optical fiber 10 of the presentembodiment, even when the outside diameter d_(f) of the glass portion 13is made smaller than 125 μm or the coating thickness t is made smallerthan 60 μm, because parameters other than the outside diameter d_(f) ofthe glass portion and the coating thickness t are adjusted so that thevalue of the microbend loss characteristic factor F_(μBL_GΔβ) is 6.1([GPa⁻¹·μm^(−2.5)/rad⁸]·10⁻¹²) or less, the microbend loss can besuppressed to the extent that the required characteristics of the tapeslot type cable are satisfied. Here, as shown in FIG. 3, the outsidediameter 2R₅ of the optical fiber 10 is represented by

2R _(s) =d _(f)+2t

using the outside diameter d_(f) of the glass portion and the coatingthickness t. Therefore, as described above, the diameter of the opticalfiber can be reduced by reducing the coating thickness t and the outsidediameter d_(f) of the glass portion. Therefore, by using the opticalfiber 10 whose diameter is reduced and microbend loss is suppressed inthis way, a tape slot type cable having excellent opticalcharacteristics that realizes an increase in the number of cores and asmall size can be configured.

Second Embodiment

Next, the second embodiment will be described with reference to FIG. 4.FIG. 4 is a diagram schematically showing a structure of a cross sectionperpendicular to a longitudinal direction of an optical fiber cable 2according to the present embodiment. Note that the same or equivalentcomponents as those of the first embodiment are designated by the samereference numerals and duplicated description will be omitted unlessotherwise specified.

As shown in FIG. 4, the optical fiber cable 2 of the present embodimenthas the same configuration as the optical fiber cable 1 of the firstembodiment in that tape core wires 4 having substantially the sameconfiguration as that of the first embodiment are accommodated inside.However, the optical fiber cable 2 is mainly different from the opticalfiber cable 1 on the points described below.

The optical fiber cable 1 is a tape slot type cable (RSCC) as describedabove. On the other hand, as shown in FIG. 4, the optical fiber cable 2of the present embodiment does not have the holding body 5. That is, theoptical fiber cable 2 is a so-called small-diameter high-density cable(UHDC: Ultra-High Density Cable) in which the tape core wires are notaccommodated in the slots of the holding body but are directlyaccommodated in the sheath. That is, an accommodation space 3S is formedinside the sheath 3 of the optical fiber cable 2, and a plurality oftape core wires 4 are arranged in the accommodation space 3S. Note thatthe tensile strength bodies 6 may be embedded in the sheath 3 of theoptical fiber cable 2 at positions facing each other across the centerof the optical fiber cable 2.

Furthermore, as described above, the tape core wire 4 of the presentembodiment has substantially the same configuration as the tape corewire 4 of the first embodiment. However, the value of the microbend losscharacteristic factor F_(μBL_GΔβ) of the optical fiber 10 included inthe tape core wire 4 of the present embodiment is 4.1([GPa⁻¹·μm^(−2.5)/rad⁸]·10⁻¹²) or less for the reason described later.

Since the small-diameter high-density cable such as the optical fibercable 2 does not have the holding body 5 as described above and isslotless, the tape core wires 4 can be densely arranged in theaccommodation space 3S of the sheath 3. Therefore, a large number oftape core wires can be accommodated as compared with the tape slot typecable such as the optical fiber cable 1.

On the other hand, in the small-diameter high-density cable, since manytape core wires are densely arranged in one place as described above, alarge lateral pressure tends to be applied to the optical fiber ascompared with the tape slot type cable. Therefore, in the small-diameterhigh-density cable, it is recommended to use an optical fiber having asmaller microbend loss than the optical fiber used for the tape slottype cable. In view of the above, the small-diameter high-density cablehas the required characteristics that the value of the aforementionedsandpaper tension winding loss increase is 0.34 dB/km or less.

The present inventor has calculated the value of the microbend losscharacteristic factor F_(μBL_GΔβ) corresponding to the value (0.34dB/km) of the sandpaper tension winding loss increase on the basis ofthe aforementioned formulae (3) to (5) and found that the value is 4.1([GPa⁻¹·μm^(−2.5)/rad⁸]·10⁻¹²). That is, it has been found that bysetting the value of the microbend loss characteristic factorF_(μBL_GΔβ) to 4.1 ([GPa⁻¹·μm^(−2.5)/rad⁸]·10⁻¹²) or less, the microbendloss can be suppressed to the extent that the required characteristicsof the small-diameter high-density cable are satisfied.

As described above, the optical fiber 10 of the present embodiment isconfigured so that the aforementioned various parameters are adjusted sothat the value of the microbend loss characteristic factor F_(μBL_GΔβ)is 4.1 ([GPa⁻¹·μm^(−2.5)/rad⁸]·10⁻¹²) or less. Therefore, the microbendloss can be suppressed to the extent that the required characteristicsof the small-diameter high-density cable are satisfied. Therefore, theoptical fiber cable 2 using the optical fiber 10 can exhibit favorableoptical characteristics.

Furthermore, as described above, in the optical fiber 10 of the presentembodiment, even when the optical fiber 10 has a reduced diameter bymaking the outside diameter d_(f) of the glass portion 13 smaller than125 μm and the coating thickness t smaller than 60 μm, the microbendloss can be suppressed to the extent that the required characteristicsof the small-diameter high-density cable are satisfied. Therefore, byusing the optical fiber 10 whose diameter is reduced in this way, asmall-diameter high-density cable having excellent opticalcharacteristics that realizes an increase in the number of cores and asmall size can be configured.

Next, the reason why the outside diameter d_(f) of the glass portion 13can be small, the reason why the coating thickness of the optical fiber10 can be small, the reason why the outside diameter of the opticalfiber 10 can be small, and the like will be described.

The present inventor performed the following Examples 1 to 48 in orderto verify the relationship between the value of the microbend losscharacteristic factor F_(μBL_GΔβ) and the value of the sandpaper tensionwinding loss increase α_(μBL). Note that aspects for carrying out thepresent invention are not limited to Examples 1 to 48.

Examples 1 to 22

The present inventor prepared Samples 1 to 22 of optical fiber in whichthe aforementioned various parameters were changed, measured the valueof sandpaper tension winding loss increase for each of Samples 1 to 22,and calculated the value of the microbend loss characteristic factorF_(μBL_GΔβ) on the basis of the aforementioned formulae (3) to (5). Theoptical fiber of Sample 1 is the optical fiber of Example 1, and theoptical fiber of Sample 2 is the optical fiber of Example 2. Thus, thesample numbers of the optical fibers correspond to the numbers of theExamples. Note that the optical fiber of Sample 8 is an optical fibergenerally used for an optical fiber cable constituting the communicationinfrastructures, and has an outside diameter of the glass portion of 125μm and a coating thickness of 57.5 μm. The optical fiber of Sample 8 maybe referred to as the “general optical fiber”.

The test for sandpaper tension winding loss increase was performed inthe manner described below. That is, first, sandpaper (SiC having anaverage particle diameter of 50 μm (for example, model number #360)) waswound around the bobbin body portion having a body diameter of 380 mm,and one layer of optical fiber wire was wound therearound at 100 gf, andlight having a wavelength of 1550 nm was caused to propagate. Thetransmission loss at this time was measured. Thereafter, the opticalfiber wire was unwound from the bobbin, light having a wavelength of1550 nm was caused to propagate with almost no tension applied, and thetransmission loss was measured. Then, the difference between thesetransmission losses was obtained, and the value of this difference wasdefined as sandpaper tension winding loss increase α_(μBL).

Tables 1 to 5 below show the parameter specifications for each ofSamples 1 to 22, the values of the microbend loss characteristic factorF_(μBL_GΔβ) for each of Samples 1 to 22, and the values of the sandpapertension winding loss increase α_(μBL) for each of Samples 1 to 22.

Note that in Tables 1 to 5 below and Tables 7 to 10 described below,mode field diameter (MFD), cutoff wavelength, macrobend loss, and thelike are as described below. The mode field diameter is the mode fielddiameter of light in the LP01 mode when light having a wavelength of1310 nm is caused to propagate through the optical fiber.

Note that the mode field diameter is expressed by Petermann IIdefinition formula (formula (6) below) in ITU-T Recommendation G.650.1.Here, E(r) represents the electric field strength at the point where thedistance from the central axis of the optical fiber is r.

$\begin{matrix}{{MFD} = {{2w} = {2\sqrt{\frac{2{\int\limits_{0}^{\infty}{{E^{2}(r)}{rdr}}}}{\int\limits_{0}^{\infty}{\left\lbrack {{{dE}(r)}/{dr}} \right\rbrack^{2}{rdr}}}}}}} & (6)\end{matrix}$

Furthermore, the aforementioned cutoff wavelength indicates the minimumwavelength at which the high-order mode is sufficiently attenuated. Thishigh-order mode refers to, for example, LP11 mode. Specifically, it isthe minimum wavelength at which the loss of the high-order mode is 19.3dB. The cutoff wavelength includes a fiber cutoff wavelength and a cablecutoff wavelength, and can be measured by, for example, the measurementmethod described in ITU-T Recommendation G.650. The cutoff wavelengthsdescribed in Tables 1 to 5 are cable cutoff wavelengths. Furthermore,the MAC value is the ratio of the mode field diameter of light at awavelength of 1310 nm to the cable cutoff wavelength, and is defined as2w/λ_(cc) when the mode field diameter is defined as 2w and the cablecutoff wavelength is defined as λ_(cc). Furthermore, the macrobendlosses are the bend loss caused by light having a wavelength of 1625 nmpropagating through a bent portion formed when the optical fiber is bentwith a radius of 10 mm. The unit “/turn” of macrobend loss means “perturn of optical fiber”. Furthermore, the propagation constant differenceis the difference between the propagation constant of light having awavelength of 1550 nm in the waveguide mode and the propagation constantof light having a wavelength of 1550 in the radiation mode, and, in thisexperiment, is the difference between the propagation constant of lighthaving a wavelength of 1550 nm in the LP01 mode and the propagationconstant in the LP11 mode. The propagation constant was calculated usingthe two-dimensional finite element method described in Non-PatentLiterature 7 (K. Saitoh and M. Koshiba, “Full-VectorialImaginary-Distance Beam Propagation Method Based on a Finite ElementScheme: Application to Photonic Crystal Fibers,” IEEE J. Quant. Elect.vol. 38, pp. 9 27-933, 2002.) on the basis of the refractive indexprofile of a prototyped optical fiber. Furthermore, the zero dispersionwavelength refers to a wavelength at which the value of the wavelengthdispersion becomes zero. Here, the wavelength dispersion is the sum ofmaterial dispersion and waveguide dispersion. Furthermore, the zerodispersion slope refers to the rate of change of wavelength dispersionwith respect to the wavelength at the zero dispersion wavelength.

TABLE 1 Example 1 2 3 4 5 Outside diameter of 80 80 80 125 80 glassportion(μm) Outside diameter of 125 115 115 159 115 primary coatinglayer(μm) Outside diameter of 156 152 164 193 153 secondary coatinglayer(μm) Young's modulus of 74 74 74 74 74 glass portion(GPa) Young'smodulus of 0.2 0.2 0.2 0.5 0.2 primary coating layer(MPa) Young'smodulus of 1150 1400 1400 1150 1400 secondary coating layer(MPa)Thickness of primary 22.5 17.5 17.5 17 17.5 coating layer(μm) Thicknessof secondary 15.5 18.5 24.5 17 19 coating layer(μm) Coatingthickness(μm) 38 36 42 34 36.5 Bending rigidity of 1.49 × 10¹¹ 1.49 ×10¹¹ 1.49 × 10¹¹ 8.87 × 10¹¹ 1.49 × 10¹¹ glass portion(MPa · μm⁴)Bending rigidity of 1.97 × 10¹⁰ 2.47 × 10¹⁰ 3.77 × 10¹⁰ 4.22 × 10¹⁰ 2.56× 10¹⁰ secondary coating layer(MPa · μm⁴) μ (a.u.) 3 3 3 3 3 κ_(s)(MPa)0.71 0.91 0.91 3.68 0.91 Deformation resistance of 9.22 20.39 37.54 6.7921.65 secondary coating layer(MPa) F_(μ BL) _(—) _(G)(GPa⁻¹ · μm^(−10.5)· 3.66 3.90 2.38 1.92 3.72 10⁻²⁷) Mode field diameter(μm) 8.83 8.66 8.668.6 8.6 Cable cutoff wavelength(μm) 1.230 1.230 1.230 1.230 1.200 MACvalue(a.u.) 7.18 7.04 7.04 6.99 7.17 Macrobend loss(dB/turn) 0.100 0.0500.050 0.050 0.200 Propagation constant 12498 13182 13182 13066 11613difference (rad/m) Zero dispersion 1.311 1.316 1.316 1.317 1.310wavelength(μm) Zero dispersion 0.088 0.086 0.086 0.086 0.087slope(ps/km/nm²) F_(μ BL) _(—) _(Δ β)(1/rad/μm)⁸) 1.68 × 10¹⁵ 1.10 ×10¹⁵ 1.10 × 10¹⁵ 1.18 × 10¹⁵ 3.02 × 10¹⁵ F_(μ BL) _(—) _(GΔ β) 6.15 4.282.61 2.25 11.25 ([GPa⁻¹ · μm^(−2.5)/rad⁸] × 10⁻¹²) Sandpaper tensionwinding 0.85 0.46 0.3 0.22 0.98 loss increase (dB/km)

TABLE 2 Example 6 7 8 9 10 Outside diameter of 80 125 125 80 80 glassportion(μm) Outside diameter of 115 159 190 113 113 primary coatinglayer(μm) Outside diameter of 153 193 240 164 153 secondary coatinglayer(μm) Young's modulus of 74 74 74 114 74 glass portion(GPa) Young'smodulus of 0.2 0.5 0.6 0.2 0.2 primary coating layer(MPa) Young'smodulus of 1150 1150 800 1150 1150 secondary coating layer(MPa)Thickness of primary 17.5 17 32.5 16.5 16.5 coating layer(μm) Thicknessof secondary 19 17 25 25.5 20 coating layer(μm) Coating thickness(μm)36.5 34 57.5 42 36.5 Bending rigidity of 1.49 × 10¹¹ 8.87 × 10¹¹ 8.87 ×10¹¹ 2.29 × 10¹¹ 1.49 × 10¹¹ glass portion(MPa · μm⁴) Bending rigidityof 2.11 × 10¹⁰ 4.22 × 10¹⁰ 7.91 × 10¹⁰ 3.16 × 10¹⁰ 2.17 × 10¹⁰ secondarycoating layer(MPa · μm⁴) μ (a.u.) 3 3 3 3 3 κ_(s)(MPa) 0.91 3.68 2.310.97 0.97 Deformation resistance of 17.82 6.79 7.83 34.78 20.75secondary coating layer(MPa) F_(μ BL) _(—) _(G)(GPa⁻¹ · μm^(−10.5) ·4.53 1.92 0.48 1.29 4.72 10⁻²⁷) Mode field diameter(μm) 8.48 8.5 8.558.51 8.47 Cable cutoff wavelength(μm) 1.209 1.203 1.197 1.287 1.330 MACvalue(a.u.) 7.01 7.07 7.14 6.61 6.37 Macrobend loss(dB/turn) 0.200 0.0910.133 0.013 0.035 Propagation constant 11403 11971 11623 14259 14296difference (rad/m) Zero dispersion 1.313 1.313 1.313 1.309 1.309wavelength(μm) Zero dispersion 0.085 0.086 0.086 0.091 0.091slope(ps/km/nm²) F_(μ BL) _(—) _(Δ β)(1/(rad/μm)⁸) 3.50 × 10¹⁵ 2.37 ×10¹⁵ 3.00 × 10¹⁵ 5.85 × 10¹⁴ 5.73 × 10¹⁴ F_(μ BL) _(—) _(GΔ β) 15.834.54 1.45 0.76 2.70 ([GPa⁻¹ · μm^(−2.5)/rad⁸] × 10⁻¹²) Sandpaper tensionwinding 1.5 0.3 0.05 0.218 0.315 loss increase (dB/km)

TABLE 3 Example 11 12 13 14 15 Outside diameter of 80 80 80 80 90 glassportion(μm) Outside diameter of 114 114 115 115 121 primary coatinglayer(μm) Outside diameter of 153 164 153 153 159 secondary coatinglayer(μm) Young's modulus of 74 74 74 74 74 glass portion(GPa) Young'smodulus of 0.2 0.2 0.2 0.2 0.2 primary coating layer(MPa) Young'smodulus of 1150 1150 1150 1400 1150 secondary coating layer(MPa)Thickness of primary 17 17 17.5 17.5 15.5 coating layer(μm) Thickness ofsecondary 19.5 25 19 19 19 coating layer(μm) Coating thickness(μm) 36.542 36.5 36.5 34.5 Bending rigidity of 1.49 × 10¹¹ 1.49 × 10¹¹ 1.49 ×10¹¹ 1.49 × 10¹¹ 2.38 × 10¹¹ glass portion(MPa · μm⁴) Bending rigidityof 2.14 × 10¹⁰ 3.13 × 10¹⁰ 2.11 × 10¹⁰ 2.56 × 10¹⁰ 2.40 × 10¹⁰ secondarycoating layer(MPa · μm⁴) μ (a.u.) 3 3 3 3 3 κ_(s)(MPa) 0.94 0.94 0.910.91 1.16 Deformation resistance of 19.25 32.79 17.82 21.65 15.90secondary coating layer(MPa) F_(μ BL) _(—) _(G)(GPa⁻¹ · μm^(−10.5) ·4.61 2.98 4.53 3.72 2.74 10⁻²⁷) Mode field diameter(μm) 8.47 8.5 8.368.4 8.52 Cable cutoff wavelength(μm) 1.357 1.367 1.174 1.188 1.221 MACvalue(a.u.) 6.24 6.22 7.12 7.07 6.98 Macrobend loss(dB/turn) 0.010 0.0100.080 0.040 0.040 Propagation constant 15223 15007 13198 15278 14687difference (rad/m) Zero dispersion 1.309 1.309 1.310 1.310 1.309wavelength(μm) Zero dispersion 0.091 0.091 0.089 0.089 0.091slope(ps/km/nm²) F_(μ BL) _(—) _(Δ β)(1/rad/μm)⁸) 3.47 × 10¹⁴ 3.89 ×10¹⁴ 1.09 × 10¹⁵ 3.37 × 10¹⁴ 4.62 × 10¹⁴ F_(μ BL) _(—) _(GΔ β) 1.60 1.164.92 1.25 1.26 ([GPa⁻¹ · μm^(−2.5)/rad⁸] × 10⁻¹² Sandpaper tensionwinding 0.231 0.289 0.57 0.27 0.197 loss increase (dB/km)

TABLE 4 Example 16 17 18 19 20 Outside diameter of 90 90 80 80 80 glassportion(μm) Outside diameter of 121 121 115 115 115 primary coatinglayer(μm) Outside diameter of 159 159 153 164 153 secondary coatinglayer(μm) Young's modulus of 74 74 74 74 74 glass portion(GPa) Young'smodulus of 0.2 0.2 0.2 0.2 0.2 primary coating layer(MPa) Young'smodulus of 1150 1150 1150 1150 1150 secondary coating layer(MPa)Thickness of primary 15.5 15.5 17.5 17.5 17.5 coating layer(μm)Thickness of secondary 19 19 19 24.5 19 coating layer(μm) Coatingthickness(μm) 34.5 34.5 36.5 42 36.5 Bending rigidity of 2.38 × 10¹¹2.38 × 10¹¹ 1.49 × 10¹¹ 1.49 × 10¹¹ 1.49 × 10¹¹ glass portion(MPa · μm⁴)Bending rigidity of 2.40 × 10¹⁰ 2.40 × 10¹⁰ 2.11 × 10¹⁰ 3.10 × 10¹⁰ 2.11× 10¹⁰ secondary coating layer(MPa · μm⁴) μ (a.u.) 3 3 3 3 3 κ_(s)(MPa)1.16 1.16 0.91 0.91 0.91 Deformation resistance of 15.90 15.90 17.8230.87 17.82 secondary coating layer(MPa) F_(μ BL) _(—) _(G)(GPa⁻¹ ·μm^(−10.5) · 2.74 2.74 4.53 2.90 4.53 10⁻²⁷) Mode field diameter(μm)8.506 8.46 7.645 7.64 7.607 Cable cutoff wavelength(μm) 1.270 1.2861.184 1.245 1.271 MAC value(a.u.) 6.70 6.58 6.46 6.14 5.99 Macrobendloss(dB/turn) 0.017 0.008 0.070 0.006 0.004 Propagation constant 1439215187 12929 13865 14825 difference (rad/m) Zero dispersion 1.309 1.3091.336 1.336 1.336 wavelength(μm) Zero dispersion 0.091 0.091 0.079 0.0790.079 slope(ps/km/nm²) F_(μ BL) _(—) _(Δ β)(1/rad/μm)⁸) 5.43 × 10¹⁴ 3.53× 10¹⁴ 1.28 × 10¹⁵ 7.32 × 10¹⁴ 4.29 × 10¹⁴ F_(μ BL) _(—) _(GΔ β) 1.490.97 5.80 2.12 1.94 ([GPa⁻¹ · μm^(−2.5)/rad⁸] × 10⁻¹² Sandpaper tensionwinding 0.232 0.164 0.577 0.23 0.259 loss increase (dB/km)

TABLE 5 Example 21 22 Outside diameter of 80 80 glass portion(μm)Outside diameter of 115 115 primary coating layer(μm) Outside diameterof 153 153 secondary coating layer(μm) Young's modulus of 74 74 glassportion(GPa) Young's modulus of 0.2 0.2 primary coating layer(MPa)Young's modulus of 1150 1400 secondary coating layer(MPa) Thickness ofprimary 17.5 17.5 coating layer(μm) Thickness of secondary 19 19 coatinglayer(μm) Coating thickness(μm) 36.5 36.5 Bending rigidity of 1.49 ×10¹¹ 1.49 × 10¹¹ glass portion(MPa · μm⁴) Bending rigidity of 2.11 ×10¹⁰ 2.56 × 10¹⁰ secondary coating layer(MPa · μm⁴) μ (a.u.) 3 3κ_(s)(MPa) 0.91 0.91 Deformation resistance of 17.82 21.65 secondarycoating layer(MPa) F_(μ BL) _(—) _(G)(GPa⁻¹ · μm^(−10.5) · 4.53 3.7210⁻²⁷) Mode field diameter(μm) 7.627 7.7 Cable cutoff wavelength(μm)1.300 1.183 MAC value(a.u.) 5.87 6.51 Macrobend loss(dB/turn) 0.0010.040 Propagation constant 15702 13192 difference (rad/m) Zerodispersion 1.336 1.339 wavelength(μm) Zero dispersion 0.079 0.079slope(ps/km/nm²) F_(μ BL) _(—) _(Δ β)(1/rad/μm)⁸) 2.71 × 10¹⁴ 1.09 ×10¹⁵ F_(μ BL) _(—) _(GΔ β) 1.22 4.06 ([GPa⁻¹ · μm^(−2.5)/rad⁸] × 10⁻¹²Sandpaper tension winding 0.165 0.334 loss increase (dB/km)

The present inventor plotted the values of the microbend losscharacteristic factor F_(μBL_GΔβ) and the values of the sandpapertension winding loss increase α_(μBL) of each of Samples 1 to 22 withrespect to a coordinate system in which the value of microbend losscharacteristic factor F_(μBL_GΔβ) is on the horizontal axis (X-axis) andthe value of sandpaper tension winding loss increase α_(μBL) is on thevertical axis (Y-axis). As a result, the scatter diagram shown in FIG. 5was obtained. When the function was obtained from this scatter diagramusing the least-squares method, a linear function with a positive sloperepresented by the formula (7) below was obtained. Furthermore, thecorrelation coefficient of the data in FIG. 5 was 94% or more.

Y=0.0986X  (7)

That is, it was found that the value of the microbend losscharacteristic factor F_(μBL_GΔβ) and the value of the sandpaper tensionwinding loss increase α_(μBL) had a high correlation, and specificallythe value of the microbend loss characteristic factor F_(μBL_GΔβ) andthe value of the sandpaper tension winding loss increase α_(μBL) had aproportional relationship having a generally positive slope.

By the way, as described above, the tape slot type cable (RSCC) has therequired characteristics that the value of the sandpaper tension windingloss increase α_(μBL) is 0.60 (dm/km) or less. Furthermore, thesmall-diameter high-density cable (UHDC) has the requiredcharacteristics that the value of the sandpaper tension winding lossincrease α_(μBL) is 0.34 (dm/km) or less. Therefore, Table 6 belowindicates the values of the microbend loss characteristic factorF_(μBL_GΔβ), the values of the sandpaper tension winding loss increaseα_(μBL), the pass/fail of the required characteristics of the tape slottype cable (RSCC), and the pass/fail of the required characteristics ofthe small-diameter high-density cable (UHDC) of Examples 1 to 22. Notethat in Table 6, Y means that the required characteristics aresatisfied, and N means that the required characteristics are notsatisfied.

TABLE 6 F_(μ BL) _(—) _(GΔ β) α μBL ([GPa⁻¹ · μm^(−2.5)/ Application toRSCC Application to UHDC Example (dB/km) rad⁸] × 10⁻¹²) (F_(μ BL) _(—)_(GΔ β) ≤ 6.1) (F_(μ BL) _(—) _(GΔ β) ≤ 4.1) 9 0.22 0.76 Y Y 17 0.160.97 Y Y 12 0.29 1.16 Y Y 21 0.17 1.22 Y Y 14 0.27 1.25 Y Y 15 0.27 1.26Y Y 8 0.05 1.45 Y Y 16 0.23 1.49 Y Y 11 0.23 1.60 Y Y 20 0.26 1.94 Y Y19 0.23 2.12 Y Y 4 0.22 2.25 Y Y 3 0.30 2.61 Y Y 10 0.32 2.70 Y Y 220.33 4.06 Y Y 2 0.46 4.28 Y N 7 0.30 4.54 Y Y 13 0.57 4.92 Y N 18 0.585.80 Y N 1 0.85 6.15 N N 5 0.98 11.25 N N 6 1.50 15.83 N N

From Table 6, it was found that when the value of the microbend losscharacteristic factor F_(μBL_GΔβ) is 6.1 ([GPa⁻¹·μm^(−2.5)/rad⁸]·10⁻¹²)or less, the value of the sandpaper tension winding loss increaseα_(μBL) tends to be approximately 0.60 or less and when the value of themicrobend loss characteristic factor F_(μBL_GΔβ) is larger than 6.1([GPa⁻¹·μm^(−2.5)/rad⁸]·10⁻¹²), the value of the sandpaper tensionwinding loss increase α_(μBL) tends to exceed 0.60. In other words, itwas found that the required characteristics of the tape slot type cablecan be satisfied by adjusting the values of the parameters described inTables 1 to 5 described above so that the value of the microbend losscharacteristic factor F_(μBL_GΔβ) is 6.1 ([GPa⁻¹·μm^(−2.5)/rad⁸]·10⁻¹²)or less.

Furthermore, it was found that when the value of the microbend losscharacteristic factor F_(μBL_GΔβ) is 4.1 ([GPa⁻¹·μm^(−2.5)/rad⁸]·10⁻¹²)or less, the value of the sandpaper tension winding loss increaseα_(μBL) tends to be approximately 0.34 or less and when the value of themicrobend loss characteristic factor F_(μBL_GΔβ) is larger than 4.1([GPa⁻¹·μm^(−2.5)/rad⁸]·10⁻¹²), the value of the sandpaper tensionwinding loss increase α_(μBL) tends to exceed 0.34. In other words, itwas found that in addition to the required characteristics of the tapeslot type cable, the required characteristics of the small-diameterhigh-density cable can be satisfied by adjusting the values of theparameters described in Tables 1 to 5 described above so that the valueof the microbend loss characteristic factor F_(μBL_GΔβ) is 4.1([GPa⁻¹·μm^(−2.5)/rad⁸]·10⁻¹²) or less.

Specifically, among Samples 1 to 22, the samples satisfying the requiredcharacteristics of the tape slot type cable were the samples excludingSamples 1, 5, and 6. Furthermore, the samples satisfying the requiredcharacteristics of the small-diameter high-density cable in addition tothe required characteristics of the tape slot type cable were thesamples excluding Examples 1, 2, 5, 6, 13, and 18.

Furthermore, among the samples satisfying at least the requiredcharacteristics of the tape slot type cable among Samples 1 to 22, thesamples excluding Samples 4, 7, and 8 have an outside diameter of theglass portion of 80 μm or 90 μm smaller than the outside diameter (125μm) of the glass portion of the general optical fiber. Specifically,Samples 2, 3, 9 to 14, and 18 to 22 have an outside diameter of theglass portion of 80 μm, and Samples 15 to 17 have an outside diameter ofthe glass portion of 90 μm. That is, it was found that, by adjusting theparameters as in Samples 2, 3, and 9 to 22, an optical fiber thatsatisfies at least the required characteristics of the tape slot typecable and has the outside diameter of the glass portion smaller thanthat of the general optical fiber can be formed.

Furthermore, it was found that the samples, excluding Sample 8,satisfying at least the required characteristics of the tape slot typecable among Samples 1 to 22 have a coating thickness smaller than thecoating thickness (approximately 60 μm) of the general optical fiber.Specifically, it was found that Samples 3, 9, and 12 have a coatingthickness of 42.0 μm, Samples 10, 11, 13, 14, 18, and 20 to 22 have acoating thickness of 36.5 μm, Sample 2 has a coating thickness of 36.0μm, Samples 15 to 17 have a coating thickness of 34.5 μm, and Samples 4and 7 have a coating thickness of 34.0 μm. That is, it was found that,by adjusting the parameters as in Samples 2 to 4, 7, and 9 to 22, anoptical fiber that satisfies at least the required characteristics ofthe tape slot type cable and has the coating thickness smaller than thatof the general optical fiber can be formed.

As described above, it was found that, among Samples 1 to 22, thesamples excluding Samples 1, 5, 6, and 8 satisfy at least the requiredcharacteristics of the tape slot type cable and have the outsidediameter of the glass portion and the coating thickness smaller thanthose of the general optical fiber. By forming both the outside diameterof the glass portion and the coating thickness to be smaller than theoutside diameter of the glass portion and the coating thickness of thegeneral optical fiber, it is possible to effectively realize a reductionin diameter of the optical fiber.

Furthermore, the optical fibers of Samples 1 to 22 have an MFD of 7.6 μmor more. When the MFD is too small, an MFD mismatch can occur whenconnection to a general-purpose optical fiber is established. However,when the MFD of the optical fiber is 7.6 μm or more, the MFD mismatchwhen connection to a general-purpose optical fiber is established can besmall. Therefore, the occurrence of connection loss can be effectivelysuppressed.

Moreover, the optical fibers of Samples 5 to 8 meet the internationalstandard ITU-.G.657.A1. That is, the MFD at a wavelength of 1310 nm is8.2 μm or more and 9.6 μm or less, the cable cutoff wavelength is 1260nm or less, the zero dispersion wavelength is 1300 nm or more and 1324nm or less, the zero dispersion slope is 0.073 ps/km/nm or more and0.092 ps/km/nm or less, and the macrobend loss at a wavelength of 1625nm by bending at a radius of 10 mm is 1.5 dB/turn or less. Furthermore,the optical fibers of Samples 1 to 4 satisfy ITU-T.G.657.A2. That is,the MFD at a wavelength of 1310 nm is 8.2 μm or more and 9.6 μm or less,the cable cutoff wavelength is 1260 nm or less, the zero dispersionwavelength is 1300 nm or more and 1324 nm or less, the zero dispersionslope is 0.073 ps/km/nm or more and 0.092 ps/km/nm or less, and themacrobend loss at a wavelength of 1625 nm by bending at a radius of 10mm is 0.2 dB/turn or less. Furthermore, the optical fibers of Samples 13to 15 satisfy ITU-T.G.657.B3. That is, the MFD at a wavelength of 1310nm is 8.26 μm or more and 9.6 μm or less, the cable cutoff wavelength is1260 nm or less, the zero dispersion wavelength is 1300 nm or more and1324 nm, the zero dispersion slope is 0.073 ps/km/nm or more and 0.092ps/km/nm or less, and the macrobend loss at a wavelength of 1625 nm bybending at a radius of 10 mm is 0.1 dB/turn or less.

Examples 23 to 28

Furthermore, the present inventor determined the values of the microbendloss characteristic factor F_(μBL_GΔβ) of Samples 23 to 28 of opticalfiber adjusted as indicated in Table 7 below on the assumption of anoptical fiber having the same optical characteristics as Samples 16, 17,and 19, specifically, the same MFD, cable cutoff wavelength, MAC value,macrobend loss (bending loss), propagation constant difference, zerodispersion wavelength, and zero dispersion slope as those samples, thesame thickness of the primary coating layer and thickness of thesecondary coating layer as those of Sample 19, and an outside diameterof the glass portion of 65 μm.

TABLE 7 Example 23 24 25 26 27 28 Outside diameter of 65 65 65 65 65 65glass portion(μm) Outside diameter of 100 100 100 100 100 100 primarycoating layer(μm) Outside diameter of 149 149 149 149 149 149 secondarycoating layer(μm) Young's modulus of 74 74 74 74 74 74 glassportion(GPa) Young's modulus of 0.2 0.2 0.2 0.2 0.2 0.2 primary coatinglayer(MPa) Young's modulus of 1400 1150 1400 1150 1400 1150 secondarycoating layer(MPa) Thickness of primary 17.5 17.5 17.5 17.5 17.5 17.5coating layer(μm) Thickness of secondary 24.5 24.5 24.5 24.5 24.5 24.5coating layer(μm) Coating thickness(μm) 42 42 42 42 42 42 Bendingrigidity of 6.48 × 10¹⁰ 6.48 × 10¹⁰ 6.48 × 10¹⁰ 6.48 × 10¹⁰ 6.48 × 10¹⁰6.48 × 10¹⁰ glass portion(MPa · μm⁴) Bending rigidity of 2.70 × 10¹⁰2.22 × 10¹⁰ 2.70 × 10¹⁰ 2.22 × 10¹⁰ 2.70 × 10¹⁰ 2.22 × 10¹⁰ secondarycoating layer(MPa · μm⁴) μ (a.u.) 3 3 3 3 3 3 κ_(s)(MPa) 0.74 0.74 0.740.74 0.56 0.56 Deformation resistance of 49.99 41.10 49.99 41.10 49.9441.05 secondary coating layer(MPa) F_(μ BL) _(—) _(G)(GPa⁻¹ · μm^(−10.5)· 9.15 11.14 9.15 11.14 5.15 6.27 10⁻²⁷) Mode field diameter(μm) 7.647.64 8.506 8.506 8.46 8.46 Cable cutoff wavelength(μm) 1.245 1.245 1.2701.270 1.286 1.286 MAC value(a.u.) 6.14 6.14 6.70 6.70 6.58 6.58Macrobend loss(dB/turn) 0.006 0.006 0.017 0.017 0.008 0.008 Propagationconstant 13865 13865 14392 14392 15187 15187 difference (rad/m) Zerodispersion 1.336 1.336 1.309 1.309 1.309 1.309 wavelength(μm) Zerodispersion 0.079 0.079 0.091 0.091 0.091 0.091 slope(ps/km/nm²) F_(μ BL)_(—) _(Δ β)(1/rad/μm)⁸) 7.32 × 10¹⁴ 7.32 × 10¹⁴ 5.43 × 10¹⁴ 5.43 × 10¹⁴3.53 × 10¹⁴ 3.53 × 10¹⁴ F_(μ BL) _(—) _(GΔ β) 6.70 8.15 4.97 6.05 1.822.21 ([GPa⁻¹ · μm^(−2.5)/rad⁸] × 10⁻¹²) Application to RSCC N N Y Y Y YApplication to UHDC N N N N Y Y

As indicated in Table 7, each of Samples 23 to 28 has an outsidediameter of the glass portion of 65 μm and a coating thickness of 42 μm.It was found that the values of the microbend loss characteristic factorF_(μBL_GΔβ) of Samples 25 to 28 are all 6.1([GPa⁻¹·μm^(−2.5)/rad⁸]·10⁻¹²) or less, and Samples 25 to 28 satisfy therequired characteristics of the tape slot type cable. Furthermore, itwas found that the values of the microbend loss characteristic factorF_(μBL_GΔβ) of Samples 27 and 28 are 4.1 ([GPa⁻¹·μm^(−2.5)/rad⁸]·10⁻¹²)or less, and Samples 27 and 28 satisfy the required characteristics ofthe small-diameter high-density cable in addition to the requiredcharacteristics of the tape slot type cable. Note that similar toSamples 25 to 28, Samples 23 and 24 have an outside diameter of theglass portion of 65 μm and a thickness of the coating layer of 42 μm,but the values of the microbend loss characteristic factor F_(μBL_GΔβ)exceed 6.1 ([GPa⁻¹·μm^(−2.5)/rad⁸]·10⁻¹²), and do not satisfy therequired characteristics of the tape slot type cable or the requiredcharacteristics of the small-diameter high-density cable.

Examples 29 to 36

Furthermore, the present inventor determined the values of the microbendloss characteristic factor F_(μBL_GΔβ) of Samples 29 to 36 of opticalfiber adjusted as indicated in Tables 8 and 9 on the assumption of anoptical fiber having the same optical characteristics as Samples 15, 16,17, and 19, specifically, the same MFD, cable cutoff wavelength, MACvalue, macrobend loss, propagation constant difference, zero dispersionwavelength, and zero dispersion slope as those samples, the samethickness of the primary coating layer and thickness of the secondarycoating layer as those of Sample 19, and an outside diameter of theglass portion of 70 μm.

TABLE 8 Example 29 30 31 32 Outside diameter of 70 70 70 70 glassportion(μm) Outside diameter of 105 105 105 105 primary coatinglayer(μm) Outside diameter of 154 154 154 154 secondary coatinglayer(μm) Young's modulus of 74 74 74 74 glass portion(GPa) Young'smodulus of 0.2 0.2 0.2 0.2 primary coating layer(MPa) Young's modulus of1400 1150 1400 1150 secondary coating layer(MPa) Thickness of primary17.5 17.5 17.5 17.5 coating layer(μm) Thickness of secondary 24.5 24.524.5 24.5 coating layer(μm) Coating thickness(μm) 42 42 42 42 Bendingrigidity of 8.72 × 10¹⁰ 8.72 × 10¹⁰ 8.72 × 10¹⁰ 8.72 × 10¹⁰ glassportion(MPa · μm⁴) Bending rigidity of 3.03 × 10¹⁰ 2.49 × 10¹⁰ 3.03 ×10¹⁰ 2.49 × 10¹⁰ secondary coating layer(MPa · μm⁴) μ (a.u.) 3 3 3 3κ_(s)(MPa) 0.80 0.80 0.80 0.80 Deformation resistance of 45.30 37.2445.30 37.24 secondary coating layer(MPa) F_(μ BL) _(—) _(G)(GPa⁻¹ ·μm^(−10.5) · 5.66 6.89 5.66 6.89 10⁻²⁷) Mode field diameter(μm) 7.647.64 8.52 8.52 Cable cutoff wavelength(μm) 1.245 1.245 1.221 1.221 MACvalue(a.u.) 6.14 6.14 6.98 6.98 Macrobend loss(dB/turn) 0.006 0.0060.040 0.040 Propagation constant 13865 13865 14687 14687 difference(rad/m) Zero dispersion 1.336 1.336 1.309 1.309 wavelength(μm) Zerodispersion 0.079 0.079 0.091 0.091 slope(ps/km/nm²) F_(μ BL) _(—)_(Δ β)(1/rad/μm)⁸) 7.32 × 10¹⁴ 7.32 × 10¹⁴ 4.62 × 10¹⁴ 4.62 × 10¹⁴F_(μ BL) _(—) _(GΔ β) 4.15 5.05 2.62 3.18 ([GPa⁻¹ · μm^(−2.5)/rad⁸] ×10⁻¹² Application to RSCC Y Y Y Y Application to UHDC N N Y Y

TABLE 9 Example 33 34 35 36 Outside diameter of 70 70 70 70 glassportion(μm) Outside diameter of 105 105 105 105 primary coatinglayer(μm) Outside diameter of 154 154 154 154 secondary coatinglayer(μm) Young's modulus of 74 74 74 74 glass portion(GPa) Young'smodulus of 0.2 0.2 0.2 0.2 primary coating layer(MPa) Young's modulus of1400 1150 1400 1150 secondary coating layer(MPa) Thickness of primary17.5 17.5 17.5 17.5 coating layer(μm) Thickness of secondary 24.5 24.524.5 24.5 coating layer(μm) Coating thickness(μm) 42 42 42 42 Bendingrigidity of 8.72 × 10¹⁰ 8.72 × 10¹⁰ 8.72 × 10¹⁰ 8.72 × 10¹⁰ glassportion(MPa · μm⁴) Bending rigidity of 3.03 × 10¹⁰ 2.49 × 10¹⁰ 3.03 ×10¹⁰ 2.49 × 10¹⁰ secondary coating layer(MPa · μm⁴) μ (a.u.) 3 3 3 3κ_(s)(MPa) 0.80 0.80 0.80 0.80 Deformation resistance of 45.30 37.2445.30 37.24 secondary coating layer(MPa) F_(μ BL) _(—) _(G)(GPa⁻¹ ·μm^(−10.5) · 5.66 6.89 5.66 6.89 10⁻²⁷) Mode field diameter(μm) 8.5068.506 8.46 8.46 Cable cutoff wavelength(μm) 1.270 1.270 1.286 1.286 MACvalue(a.u.) 6.70 6.70 6.58 6.58 Macrobend loss(dB/turn) 0.017 0.0170.008 0.008 Propagation constant 14392 14392 15187 15187 difference(rad/m) Zero dispersion 1.309 1.309 1.309 1.309 wavelength(μm) Zerodispersion 0.091 0.091 0.091 0.091 slope(ps/km/nm²) F_(μ BL) _(—)_(Δ β)(1/rad/μm)⁸) 5.43 × 10¹⁴ 5.43 × 10¹⁴ 3.53 × 10¹⁴ 3.53 × 10¹⁴F_(μ BL) _(—) _(GΔ β) 3.08 3.75 2.00 2.44 ([GPa⁻¹ · μm^(−2.5)/rad⁸] ×10⁻¹² Application to RSCC Y Y Y Y Application to UHDC Y Y Y Y

As indicated in Tables 8 and 9, each of Samples 29 to 36 has an outsidediameter of the glass portion of 70 μm and a coating thickness of 42 μm.It was found that the values of the microbend loss characteristic factorF_(μBL_GΔβ) of Samples 26 to 28 are all 6.1([GPa⁻¹·μm^(−2.5)/rad⁸]·10⁻¹²) or less, and Samples 29 to 36 satisfy therequired characteristics of the tape slot type cable. Furthermore, itwas found that the values of the microbend loss characteristic factorF_(μBL_GΔβ) of Samples 31, 33, 35 and 36 are all 4.1([GPa⁻¹·μm^(−2.5)/rad⁸]·10⁻¹²) or less, and Samples 31, 33, 35 and 36satisfy the required characteristics of the small-diameter high-densitycable in addition to the required characteristics of the tape slot typecable.

Examples 37 to 42

Furthermore, the present inventor determined the values of the microbendloss characteristic factor F_(μBL_GΔβ) of Samples 37 to 42 of opticalfiber adjusted as indicated in Table 10 below on the assumption of anoptical fiber having the same optical characteristics as Samples 15, 17,and 19, specifically, the same MFD, cable cutoff wavelength, MAC value,macrobend loss, propagation constant difference, zero dispersionwavelength, and zero dispersion slope as those samples, the samethickness of the primary coating layer and thickness of the secondarycoating layer as those of Sample 19, and an outside diameter of theglass portion of 75 μm.

TABLE 10 Example 37 38 39 40 41 42 Outside diameter of 75 75 75 75 75 75glass portion(μm) Outside diameter of 110 110 110 110 110 110 primarycoating layer(μm) Outside diameter of 159 159 159 159 159 159 secondarycoating layer(μm) Young's modulus of 74 74 74 74 74 74 glassportion(GPa) Young's modulus of 0.15 0.15 0.2 0.2 0.2 0.2 primarycoating layer(MPa) Young's modulus of 1400 1150 1400 1150 1400 1150secondary coating layer(MPa) Thickness of primary 17.5 17.5 17.5 17.517.5 17.5 coating layer(μm) Thickness of secondary 24.5 24.5 24.5 24.524.5 24.5 coating layer(μm) Coating thickness(μm) 42 42 42 42 42 42Bending rigidity of 1.15 × 10¹¹ 1.15 × 10¹¹ 1.15 × 10¹¹ 1.15 × 10¹¹ 1.15× 10¹¹ 1.15 × 10¹¹ glass portion(MPa · μm⁴) Bending rigidity of 3.39 ×10¹⁰ 2.78 × 10¹⁰ 3.39 × 10¹⁰ 2.78 × 10¹⁰ 3.39 × 10¹⁰ 2.78 × 10¹⁰secondary coating layer(MPa · μm⁴) μ (a.u.) 3 3 3 3 3 3 κ_(s)(MPa) 0.640.64 0.86 0.86 0.86 0.86 Deformation resistance of 41.13 33.81 41.1833.86 41.18 33.86 secondary coating layer(MPa) F_(μBL) _(—) _(G)(GPa⁻¹ ·μm^(−10.5) · 2.04 2.48 3.62 4.40 3.62 4.40 10⁻²⁷) Mode fielddiameter(μm) 7.64 7.64 8.52 8.52 8.46 8.46 Cable cutoff wavelength(μm)1.245 1.245 1.221 1.221 1.286 1.286 MAC value(a.u.) 6.14 6.14 6.98 6.986.58 6.58 Macrobend loss(dB/turn) 0.006 0.006 0.040 0.040 0.008 0.008Propagation constant 13865 13865 14687 14687 15187 15187 difference(rad/m) Zero dispersion 1.336 1.336 1.309 1.309 1.309 1.309wavelength(μm) Zero dispersion 0.079 0.079 0.091 0.091 0.091 0.091slope(ps/km/nm²) F_(μ BL) _(—) _(Δ β)(1/rad/μm)⁸) 7.32 × 10¹⁴ 7.32 ×10¹⁴ 7.32 × 10¹⁴ 4.62 × 10¹⁴ 3.53 × 10¹⁴ 3.3 × 10¹⁴ F_(μ BL) _(—)_(GΔ β) 1.49 1.82 1.67 2.03 1.28 1.56 ([GPa⁻¹ · μm^(−2.5)/rad⁸] × 10⁻¹²)Application to RSCC Y Y Y Y Y Y Application to UHDC Y Y Y Y Y Y

As indicated in Table 10, each of Samples 37 to 42 has an outsidediameter of the glass portion of 75 μm and a coating thickness of 42 μm.It was found that the values of the microbend loss characteristic factorF_(μBL_GΔβ) of Samples 37 to 42 are all 4.1([GPa⁻¹·μm^(−2.5)/rad⁸]·10⁻¹²) or less, and Samples 37 to 42 satisfy therequired characteristics of the small-diameter high-density cable inaddition to the required characteristics of the tape slot type cable.

Examples 43 to 48

Furthermore, the present inventor determined the values of the microbendloss characteristic factor F_(μBL_GΔβ) of Samples 43 to 48 of opticalfiber adjusted as indicated in Table 11 below on the assumption of anoptical fiber having the same optical characteristics as Samples 15, 17,and 19, specifically, the same MFD, cable cutoff wavelength, MAC value,macrobend loss, propagation constant difference, zero dispersionwavelength, and zero dispersion slope as those samples, the samethickness of the primary coating layer and thickness of the secondarycoating layer as those of Sample 19, and an outside diameter of theglass portion of 80 μm.

TABLE 11 Example 43 44 45 46 47 48 Outside diameter of 80 80 80 80 80 80glass portion(μm) Outside diameter of 100 100 100 100 100 100 primarycoating layer(μm) Outside diameter of 125 125 125 125 125 125 secondarycoating layer(μm) Young's modulus of 74 74 74 74 74 74 glassportion(GPa) Young's modulus of 0.12 0.12 0.12 0.12 0.12 0.12 primarycoating layer(MPa) Young's modulus of 1400 1150 1400 1150 1400 1150secondary coating layer(MPa) Thickness of primary 12.5 12.5 12.5 12.512.5 12.5 coating layer(μm) Thickness of secondary 10 10 10 10 10 10coating layer(μm) Coating thickness(μm) 22.5 22.5 22.5 22.5 22.5 22.5Bending rigidity of 1.49 × 10¹¹ 1.49 × 10¹¹ 1.49 × 10¹¹ 1.49 × 10¹¹ 1.49× 10¹¹ 1.49 × 10¹¹ glass portion(MPa · μm⁴) Bending rigidity of 8.42 ×10⁹  6.92 × 10⁹  8.42 × 10⁹  6.92 × 10⁹  8.42 × 10⁹  6.92 × 10⁹ secondary coating layer(MPa · μm⁴) μ (a.u.) 3 3 3 3 3 3 κ_(s)(MPa) 0.770.77 0.77 0.77 0.77 0.77 Deformation resistance of 5.85 4.83 5.85 4.835.85 4.83 secondary coating layer(MPa) F_(μBL) _(—) _(G)(GPa⁻¹ ·μm^(−10.5) · 8.60 10.45 8.60 10.45 8.60 10.45 10⁻²⁷) Mode fielddiameter(μm) 7.64 7.64 8.52 8.52 8.46 8.46 Cable cutoff wavelength(μm)1.245 1.245 1.221 1.221 1.286 1.286 MAC value(a.u.) 6.14 6.14 6.98 6.986.58 6.58 Macrobend loss(dB/turn) 0.006 0.006 0.040 0.040 0.008 0.008Propagation constant 13865 13865 14687 14687 15187 15187difference(rad/m) Zero dispersion 1.336 1.336 1.309 1.309 1.309 1.309wavelength(μm) Zero dispersion 0.079 0.079 0.091 0.091 0.091 0.091slope(ps/km/nm²) F_(μ BL) _(—) _(Δ β)(1/rad/μm)⁸) 7.32 × 10¹⁴ 7.32 ×10¹⁴ 4.62 × 10¹⁴ 4.62 × 10¹⁴ 3.53 × 10¹⁴ 3.53 × 10¹⁴ F_(μ BL) _(—)_(GΔ β) 6.29 7.65 3.97 4.82 3.04 3.69 ([GPa⁻¹ · μm^(−2.5)/rad⁸] × 10⁻¹²)Application to RSCC N N Y Y Y Y Application to UHDC N N Y N Y Y

As indicated in Table 11, each of Samples 45 to 48 has an outsidediameter of the glass portion of 80 μm, an outside diameter of thesecondary coating layer of 125 μm, and a thickness of the coating layerof 22.5 μm. It was found that the values of the microbend losscharacteristic factor F_(μBL_GΔβ) of Samples 45 to 48 are all 6.1([GPa⁻¹·μm^(−2.5)/rad⁸]·10⁻¹²) or less, and Samples 45 to 48 satisfy therequired characteristics of the tape slot type cable. Furthermore, itwas found that the value of the microbend loss characteristic factorF_(μBL_GΔβ) of Sample 47 is 4.1 ([GPa⁻¹·μm^(−2.5)/rad⁸]·10⁻¹²) or less,and Sample 47 satisfies the required characteristics of thesmall-diameter high-density cable in addition to the requiredcharacteristics of the tape slot type cable. Note that similar toSamples 45 to 48, Samples 43 and 44 have an outside diameter of theglass portion of 80 μm, an outside diameter of the secondary coatinglayer of 125 μm, and a thickness of the coating layer of 22.5 μm, butthe values of the microbend loss characteristic factor F_(μBL_GΔβ)exceed 6.1 ([GPa⁻¹·μm^(−2.5)/rad⁸]·10⁻¹²), and do not satisfy therequired characteristics of the tape slot type cable or the requiredcharacteristics of the small-diameter high-density cable.

Although the present invention has been described above by taking theaforementioned embodiments as an example, the present invention is notlimited thereto.

For example, in the first and second embodiments described above, theexample in which the secondary coating layer is the outermost layer ofthe optical fiber has been described. However, even when a colored layeris further provided as a third coating layer on the outer periphery ofthe secondary coating layer, the secondary coating layer and the coloredlayer can be applied to the present invention as a second coating layer,i.e., the secondary coating layer as long as the Young's modulus of thecolored layer is not significantly different from the Young's modulus ofthe secondary coating layer.

According to one or more embodiments of the present invention, anoptical fiber capable of suppressing microbend loss is provided, and canbe used in a field such as a communication infrastructure.

1. An optical fiber comprising: a glass portion including a core; a cladsurrounding the core; a primary coating layer covering the clad; and asecondary coating layer covering the primary coating layer, wherein avalue of microbend loss characteristic factor F_(μBL_GΔβ)([GPa⁻¹·μm^(−2.5)/rad⁸]·10⁻¹²) is 6.1 ([GPa⁻¹·μm^(−2.5)/rad⁸]·10⁻¹²) orless when represented byF _(μBL_GΔβ) =F _(μBL_G) ×F _(μBL_Δβ), wherein geometry microbend losscharacteristic F_(μBL_G) ([GPa⁻¹·μm^(−2.5)/rad⁸]·10⁻¹²) of the opticalfiber is represented by$F_{\mu{BL}\_ G} = \frac{{K_{s}}^{2}}{{H_{f}}^{2} \times {D_{0}}^{0.375} \times {H_{0}}^{0.625}}$${K_{s} = \frac{E_{p}d_{f}}{t_{p}}},{H_{f} = {\frac{\pi}{4}{E_{g}\left( \frac{d_{f}}{2} \right)}^{4}}},{D_{0} = {E_{p} + {\left( \frac{t_{s}}{R_{s}} \right)^{3}E_{s}}}},{H_{0} = {\frac{\pi}{4}{E_{s}\left( {{R_{s}}^{4} - {R_{p}}^{4}} \right)}}},$where κs (MPa) is a spring coefficient of the primary coating layer,H_(f) (MPa·μm⁴) is a bending rigidity of the glass portion, D₀ (MPa) isa deformation resistance of the secondary coating layer, H₀ (MPa·μm⁴) isa bending rigidity of the secondary coating layer, E_(g) (GPa) is aYoung's modulus of the glass portion, E_(p) (MPa) is a Young's modulusof the primary coating layer, E_(s) (MPa) is a Young's modulus of thesecondary coating layer, d_(f) (μm) is an outside diameter of the glassportion, R_(p) (μm) is a radius of an outer peripheral surface of theprimary coating layer, R_(s) (μm) is a radius of an outer peripheralsurface of the secondary coating layer, t_(p) (μm) is a thickness of theprimary coating layer, and t_(s) (μm) is a thickness of the secondarycoating layer, and wherein optical microbend loss characteristicF_(μBL_Δβ) (1/(rad/μm)⁸) of the optical fiber is represented by${F_{\mu{BL}{\_\Delta\beta}} = \frac{1}{({\Delta\beta})^{8}}},$ where Δβ(rad/m) is a propagation constant difference between propagationconstant of a waveguide mode propagating through the optical fiber andpropagation constant of a radiation mode.
 2. The optical fiber accordingto claim 1, wherein the value of the microbend loss characteristicfactor is 4.1 ([GPa⁻¹·μm^(−2.5)/rad⁸]·10⁻¹²) or less.
 3. The opticalfiber according to claim 1, wherein a coating thickness of a sum of thethickness of the primary coating layer and the thickness of thesecondary coating layer is 42.0 μm or less.
 4. The optical fiberaccording to claim 3, wherein the coating thickness is 38.0 μm or less.5. The optical fiber according to claim 4, wherein the coating thicknessis 36.5 μm or less.
 6. The optical fiber according to claim 5, whereinthe coating thickness is 34.5 μm or less.
 7. The optical fiber accordingto claim 6, wherein the coating thickness is 34.0 μm or less.
 8. Theoptical fiber according to claim 3, wherein the outside diameter of theglass portion is 65 μm or more and 100 μm or less.
 9. The optical fiberaccording to claim 8, wherein the outside diameter of the glass portionis 90 μm or less.
 10. The optical fiber according to claim 9, whereinthe outside diameter of the glass portion is 80 μm or less.
 11. Theoptical fiber according to claim 10, wherein the outside diameter of theglass portion is 75 μm or less.
 12. The optical fiber according to claim11, wherein the outside diameter of the glass portion is 70 μm or less.13. The optical fiber according to claim 3, wherein a mode fielddiameter of light at a wavelength of 1310 nm is 7.6 μm or more and 8.7μm or less, a cable cutoff wavelength is 1260 nm or less, zerodispersion wavelength is 1300 nm or more and 1324 nm or less, and zerodispersion slope is 0.073 ps/km/nm or more and 0.092 ps/km/nm.
 14. Theoptical fiber according to claim 13, wherein macrobend loss at awavelength of 1625 nm by bending at a radius of 10 mm is 1.5 dB/turn orless.
 15. The optical fiber according to claim 13, wherein macrobendloss at a wavelength of 1625 nm by bending at a radius of 10 mm is 0.2dB/turn or less.
 16. The optical fiber according to claim 13, whereinmacrobend loss at a wavelength of 1625 nm by bending at a radius of 10mm is 0.1 dB/turn or less.